Upgrading

    This file lists major changes between release versions that require
    ports or applications to be changed. Use it to update a port or an
    application written for an older version of lwIP to correctly work
    with newer versions.

    (git master)

      * [Enter new changes just after this line - do not remove this line]
      * The eth_addr_cmp and ip_addr_cmp set of functions have been renamed to eth_addr_eq, ip_addr_eq
        and so on, since they return non-zero on equality. Macros for the old names exist.
      * The sio_write function used by PPP now takes the data argument as const.
      * The prev field in the snmp_varbind struct has been removed.

    (2.2.0)

      ++ Repository changes:

      * The contrib repository has been added into the main repository in the subdirectory 'contrib'
        (the old contrib repository remains online for reference but is not used any more)

    (2.1.0)

      ++ Application changes:

      * Use the new altcp API for seamless TLS integration into existing TCP applications (see changelog)
      * TCP only kills existing connections with a LOWER priority than the one currently being opened.
        Previous implementations also kill existing connections of the SAME priority.
      * ip4_route_src: parameter order is reversed: ip4_route_src(dest, src) -> ip4_route_src(src, dest)
        to make parameter order consistent with other ip*_route*() functions.
        Same also applies to LWIP_HOOK_IP4_ROUTE_SRC() parameter order.
      * pbuf API: pbuf->type (an u8_t holding the enum 'pbuf_type') has changed to only hold a
        description of the pbuf (e.g. data following pbuf struct, data volatile, allocation
        source heap/pool/etc.). As a consequence, applications can't test pbuf->type any more.
        Use pbuf_match_type(pbuf, type) instead.
      * socket API: according to the standard, SO_ERROR now only returns asynchronous errors.
        All other/normal/synchronous errors are (and always were) available via 'errno'.
        LWIP_SOCKET_SET_ERRNO has been removed - 'errno' is always set - and required!
      * httpd LWIP_HTTPD_CGI_SSI: httpd_cgi_handler() has an additional parameter "struct fs_file *"

      ++ Port changes:

      * tcpip_trycallback() was renamed to tcpip_callbackmsg_trycallback() to avoid confusion
        with tcpip_try_callback()
      * compatibility headers: moved from 'src/include/posix' to 'src/include/compat/posix',
        'src/include/compat/stdc' etc.
      * The IPv6 implementation now supports address scopes. (See LWIP_IPV6_SCOPES documentation
        and ip6_zone.h for more documentation)
      * LWIP_HOOK_DHCP_APPEND_OPTIONS() has changed, see description in opt.h (options_out_len is not
        available in struct dhcp any more)
      * Added debug helper asserts to ensure threading/locking requirements are met (define
        LWIP_MARK_TCPIP_THREAD() and LWIP_ASSERT_CORE_LOCKED()).
      * Added sys_mbox_trypost_fromisr() and tcpip_callbackmsg_trycallback_fromisr()
        These can be used to post preallocated messages from an ISR to the tcpip thread
        (e.g. when using FreeRTOS)

    (2.0.2)

      ++ Application changes:

      * slipif: The way to pass serial port number has changed. netif->num is not
        supported any more, netif->state is interpreted as an u8_t port number now
        (it's not a POINTER to an u8_t any more!)

    (2.0.1)

      ++ Application changes:

      * UDP does NOT receive multicast traffic from ALL netifs on an UDP PCB bound to a specific
        netif any more. Users need to bind to IP_ADDR_ANY to receive multicast traffic and compare
        ip_current_netif() to the desired netif for every packet.
        See bug #49662 for an explanation.

    (2.0.0)

      ++ Application changes:

      * Changed netif "up" flag handling to be an administrative flag (as opposed to the previous meaning of
        "ip4-address-valid", a netif will now not be used for transmission if not up) -> even a DHCP netif
        has to be set "up" before starting the DHCP client
      * Added IPv6 support (dual-stack or IPv4/IPv6 only)
      * Changed ip_addr_t to be a union in dual-stack mode (use ip4_addr_t where referring to IPv4 only).
      * Major rewrite of SNMP (added MIB parser that creates code stubs for custom MIBs);
        supports SNMPv2c (experimental v3 support)
      * Moved some core applications from contrib repository to src/apps (and include/lwip/apps)

      +++ Raw API:
        * Changed TCP listen backlog: removed tcp_accepted(), added the function pair tcp_backlog_delayed()/
          tcp_backlog_accepted() to explicitly delay backlog handling on a connection pcb

      +++ Socket API:
        * Added an implementation for posix sendmsg()
        * Added LWIP_FIONREAD_LINUXMODE that makes ioctl/FIONREAD return the size of the next pending datagram

      ++ Port changes

      +++ new files:
        * MANY new and moved files!
        * Added src/Filelists.mk for use in Makefile projects
        * Continued moving stack-internal parts from abc.h to abc_priv.h in sub-folder "priv"
          to let abc.h only contain the actual application programmer's API

      +++ sys layer:
        * Made LWIP_TCPIP_CORE_LOCKING==1 the default as it usually performs better than
          the traditional message passing (although with LWIP_COMPAT_MUTEX you are still
          open to priority inversion, so this is not recommended any more)
        * Added LWIP_NETCONN_SEM_PER_THREAD to use one "op_completed" semaphore per thread
          instead of using one per netconn (these semaphores are used even with core locking
          enabled as some longer lasting functions like big writes still need to delay)
        * Added generalized abstraction for itoa(), strnicmp(), stricmp() and strnstr()
          in def.h (to be overridden in cc.h) instead of config
          options for netbiosns, httpd, dns, etc. ...
        * New abstraction for hton* and ntoh* functions in def.h.
          To override them, use the following in cc.h:
          #define lwip_htons(x) <your_htons>
          #define lwip_htonl(x) <your_htonl>

      +++ new options:
         * TODO

      +++ new pools:
         * Added LWIP_MEMPOOL_* (declare/init/alloc/free) to declare private memp pools
           that share memp.c code but do not have to be made global via lwippools.h
         * Added pools for IPv6, MPU_COMPATIBLE, dns-api, netif-api, etc.
         * added hook LWIP_HOOK_MEMP_AVAILABLE() to get informed when a memp pool was empty and an item
           is now available

      * Signature of LWIP_HOOK_VLAN_SET macro was changed

      * LWIP_DECLARE_MEMORY_ALIGNED() may be used to declare aligned memory buffers (mem/memp)
        or to move buffers to dedicated memory using compiler attributes

      * Standard C headers are used to define sized types and printf formatters
        (disable by setting LWIP_NO_STDINT_H=1 or LWIP_NO_INTTYPES_H=1 if your compiler
        does not support these)

      ++ Major bugfixes/improvements

      * Added IPv6 support (dual-stack or IPv4/IPv6 only)
      * Major rewrite of PPP (incl. keep-up with apache pppd)
        see doc/ppp.txt for an upgrading how-to
      * Major rewrite of SNMP (incl. MIB parser)
      * Fixed timing issues that might have lead to losing a DHCP lease
      * Made rx processing path more robust against crafted errors
      * TCP window scaling support
      * modification of api modules to support FreeRTOS-MPU (don't pass stack-pointers to other threads)
      * made DNS client more robust
      * support PBUF_REF for RX packets
      * LWIP_NETCONN_FULLDUPLEX allows netconn/sockets to be used for reading/writing from separate
        threads each (needs LWIP_NETCONN_SEM_PER_THREAD)
      * Moved and reordered stats (mainly memp/mib2)

    (1.4.0)

      ++ Application changes:

      * Replaced struct ip_addr by typedef ip_addr_t (struct ip_addr is kept for
        compatibility to old applications, but will be removed in the future).

      * Renamed mem_realloc() to mem_trim() to prevent confusion with realloc()

      +++ Raw API:
        * Changed the semantics of tcp_close() (since it was rather a
          shutdown before): Now the application does *NOT* get any calls to the recv
          callback (aside from NULL/closed) after calling tcp_close()

        * When calling tcp_abort() from a raw API TCP callback function,
          make sure you return ERR_ABRT to prevent accessing unallocated memory.
          (ERR_ABRT now means the applicaiton has called tcp_abort!)

      +++ Netconn API:
        * Changed netconn_receive() and netconn_accept() to return
          err_t, not a pointer to new data/netconn.

      +++ Socket API:
        * LWIP_SO_RCVTIMEO: when accept() or recv() time out, they
          now set errno to EWOULDBLOCK/EAGAIN, not ETIMEDOUT.

        * Added a minimal version of posix fctl() to have a
          standardised way to set O_NONBLOCK for nonblocking sockets.

      +++ all APIs:
        * correctly implemented SO(F)_REUSEADDR

      ++ Port changes

      +++ new files:

        * Added 4 new files: def.c, timers.c, timers.h, tcp_impl.h:

        * Moved stack-internal parts of tcp.h to tcp_impl.h, tcp.h now only contains
          the actual application programmer's API

        * Separated timer implementation from sys.h/.c, moved to timers.h/.c;
          Added timer implementation for NO_SYS==1, set NO_SYS_NO_TIMERS==1 if you
          still want to use your own timer implementation for NO_SYS==0 (as before).

      +++ sys layer:

        * Converted mbox- and semaphore-functions to take pointers to sys_mbox_t/
          sys_sem_t;

        * Converted sys_mbox_new/sys_sem_new to take pointers and return err_t;

        * Added Mutex concept in sys_arch (define LWIP_COMPAT_MUTEX to let sys.h use
          binary semaphores instead of mutexes - as before)

      +++ new options:

         * Don't waste memory when chaining segments, added option TCP_OVERSIZE to
           prevent creating many small pbufs when calling tcp_write with many small
           blocks of data. Instead, pbufs are allocated larger than needed and the
           space is used for later calls to tcp_write.

         * Added LWIP_NETIF_TX_SINGLE_PBUF to always copy to try to create single pbufs
           in tcp_write/udp_send.

        * Added an additional option LWIP_ETHERNET to support ethernet without ARP
          (necessary for pure PPPoE)

        * Add MEMP_SEPARATE_POOLS to place memory pools in separate arrays. This may
          be used to place these pools into user-defined memory by using external
          declaration.

        * Added TCP_SNDQUEUELOWAT corresponding to TCP_SNDLOWAT

      +++ new pools:

         * Netdb uses a memp pool for allocating memory when getaddrinfo() is called,
           so MEMP_NUM_NETDB has to be set accordingly.

         * DNS_LOCAL_HOSTLIST_IS_DYNAMIC uses a memp pool instead of the heap, so
           MEMP_NUM_LOCALHOSTLIST has to be set accordingly.

         * Snmp-agent uses a memp pools instead of the heap, so MEMP_NUM_SNMP_* have
           to be set accordingly.

         * PPPoE uses a MEMP pool instead of the heap, so MEMP_NUM_PPPOE_INTERFACES
           has to be set accordingly

      * Integrated loopif into netif.c - loopif does not have to be created by the
        port any more, just define LWIP_HAVE_LOOPIF to 1.

      * Added define LWIP_RAND() for lwip-wide randomization (needs to be defined
        in cc.h, e.g. used by igmp)

      * Added printf-formatter X8_F to printf u8_t as hex

      * The heap now may be moved to user-defined memory by defining
        LWIP_RAM_HEAP_POINTER as a void pointer to that memory's address

      * added autoip_set_struct() and dhcp_set_struct() to let autoip and dhcp work
        with user-allocated structs instead of calling mem_malloc

      * Added const char* name to mem- and memp-stats for easier debugging.

      * Calculate the TCP/UDP checksum while copying to only fetch data once:
        Define LWIP_CHKSUM_COPY to a memcpy-like function that returns the checksum

      * Added SO_REUSE_RXTOALL to pass received UDP broadcast/multicast packets to
        more than one pcb.

      * Changed the semantics of ARP_QUEUEING==0: ARP_QUEUEING now cannot be turned
        off any more, if this is set to 0, only one packet (the most recent one) is
        queued (like demanded by RFC 1122).

      ++ Major bugfixes/improvements

      * Implemented tcp_shutdown() to only shut down one end of a connection
      * Implemented shutdown() at socket- and netconn-level
      * Added errorset support to select() + improved select speed overhead
      * Merged pppd to v2.3.11 (including some backported bugfixes from 2.4.x)
      * Added timer implementation for NO_SYS==1 (may be disabled with NO_SYS_NO_TIMERS==1
      * Use macros defined in ip_addr.h to work with IP addresses
      * Implemented many nonblocking socket/netconn functions
      * Fixed ARP input processing: only add a new entry if a request was directed as us
      * mem_realloc() to mem_trim() to prevent confusion with realloc()
      * Some improvements for AutoIP (don't route/forward link-local addresses, don't break
        existing connections when assigning a routable address)
      * Correctly handle remote side overrunning our rcv_wnd in ooseq case
      * Removed packing from ip_addr_t, the packed version is now only used in protocol headers
      * Corrected PBUF_POOL_BUFSIZE for ports where ETH_PAD_SIZE > 0
      * Added support for static ARP table entries

    (STABLE-1.3.2)

      * initial version of this file